U.S. patent number 5,005,025 [Application Number 07/566,311] was granted by the patent office on 1991-04-02 for printer having means for heating a recording sheet and fixing ink thereon.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Hiroyuki Inoue, Akira Miyakawa.
United States Patent |
5,005,025 |
Miyakawa , et al. |
April 2, 1991 |
**Please see images for:
( Certificate of Correction ) ** |
Printer having means for heating a recording sheet and fixing ink
thereon
Abstract
An ink jet recording apparatus for recording by infiltrated ink
into a recording sheet or by fixing ink through evaporation of an
ink solvent includes an ink jet recording head for ejecting ink
onto the recording sheet at a recording area of the apparatus where
the recording head is opposed to the recording sheet. The apparatus
also includes a heating member extending both upstream and
downstream with respect to the recording area and a conveying
direction of the recording sheet. The heating member contacts the
recording sheet to assist in the fixation of the ink. The apparatus
further includes a press plate, disposed upstream of the recording
area with respect to a conveying route of the recording sheet, for
pressing the recording sheet against the heating member. The press
plate has a portion opposed to the heating member and a plurality
of slits spaced apart from each in a direction perpendicular to the
conveying direction of the recording sheet. The apparatus also
includes a conveying member for discharging the recording sheet
from the printer. The conveying member is provided downstream of
the recording area with respect to the conveying direction. The
heating member extends to a position opposed to the conveying
member.
Inventors: |
Miyakawa; Akira (Tanashi,
JP), Inoue; Hiroyuki (Chiba, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
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Family
ID: |
26477245 |
Appl.
No.: |
07/566,311 |
Filed: |
August 13, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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202568 |
Jun 6, 1988 |
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Foreign Application Priority Data
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Jun 12, 1987 [JP] |
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62-146376 |
Jul 7, 1987 [JP] |
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62-167827 |
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Current U.S.
Class: |
346/25;
101/424.1; 347/102 |
Current CPC
Class: |
B41J
11/0024 (20210101); B41J 11/002 (20130101) |
Current International
Class: |
B41J
11/00 (20060101); B41V 002/01 () |
Field of
Search: |
;346/25,140,75
;101/424.1,487,488 ;400/126,645-645.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2717119 |
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Oct 1977 |
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DE |
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56-56891 |
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May 1981 |
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JP |
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120447 |
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Jul 1982 |
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JP |
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58-82762 |
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May 1983 |
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JP |
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59-220385 |
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Dec 1984 |
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JP |
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61-32758 |
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Feb 1986 |
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JP |
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130863 |
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Jun 1987 |
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JP |
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Primary Examiner: Hartary; Joseph W.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Parent Case Text
This application is a continuation of application Ser. No
07/202,568 filed June 6, 1988, now abandoned.
Claims
We claim:
1. A printer comprising:
ink jet recording means for recording on a recording sheet;
means for providing a conveyance route for conveying the recording
sheet through a recording area where said recording means is
opposed to the recording sheet and records on the recording sheet,
said means comprising a heating member for contacting the recording
sheet to heat the recording sheet; and
a press plate, disposed upstream of the recording area with respect
to the conveying route, for pressing the recording sheet to said
heating member, said press plate having a portion opposed to said
heating member and a plurality of spaced apart slots spaced apart
from each other in a direction perpendicular to a conveying
direction of the recording sheet.
2. A printer according to claim 1, wherein said press plate has
spring characteristics and contacts said heating member.
3. A printer according to claim 1, wherein said providing means
further comprises a conveying member for discharging the recording
sheet from the printer provided downstream of said recording area
with respect to said conveying direction and wherein said heating
member extends to a position opposed to said conveying member.
4. A printer according to claim 1, further comprising suction means
for adhering the recording sheet to said heating member and wherein
said suction means applies a suction force on a reverse side of
said heating member with respect to a conveying surface of the
recording sheet.
5. A printer according to claim 1, wherein said plurality of slots
of said press plate are provided on a side end of said press plate
on the upstream portion of said press plate with respect to said
conveying direction and partially separate said side end from the
rest of said press plate.
6. A printer according to claim 1, wherein said heating member has
a temperature ranging from 40.degree. C. to 100.degree. C.
7. A printer according to claim 1, wherein said heating member has
a temperature ranging from 30.degree. C. to 150.degree. C. and
wherein said recording means includes an ink jet recording
head.
8. A printer according to claim 7, wherein said providing means
further comprises a conveying member for discharging the recording
sheet from the printers provided downstream of the recording area
with respect to said conveying direction and wherein said heating
member extends to a position opposed to said conveying member.
9. A printer according to claim 1, wherein said plurality of slots
of said press plate are provided on a side end of said press plate
on the downstream portion of said press plate with respect to said
conveying direction and partially separate from said side end from
the rest of said press plate.
10. A printer according to claim 9, wherein the length of said
plurality of slots is half the width of said press plate with
respect to said conveying direction.
11. A printer according to claim 9, wherein said press plate has
spring characteristics and contacts said heating member.
12. A printer according to claim 9, wherein said providing means
further comprises a conveying member for discharging the recording
sheet from said printer provided downstream of said recording area
with respect to said conveying direction and said heating member
extends to a position opposed to said conveying member.
13. An ink jet recording apparatus for recording by infiltrating
ink into a recording sheet or fixing ink through the evaporation of
an ink solvent, said apparatus comprising:
an ink jet recording head for ejecting ink onto the recording sheet
along a scanning direction across the width of the recording sheet
at a recording area of said apparatus where said recording head is
opposed to the recording sheet;
a heating member extending both upstream and downstream with
respect to said recording area and a conveying direction of the
recording sheet, wherein said heating member contacts the recording
sheet to assist in fixation of the ink;
a press plate, disposed upstream of said recording area with
respect to a conveying route of the recording sheet, for pressing
the recording sheet against said heating member, said press plate
having a portion opposed to said heating member and a plurality of
slots spaced apart from each other with respect to the scanning
direction; and
a conveying member for discharging the recording sheet from said
apparatus provided downstream of said recording area with respect
to the conveying direction and wherein said heating member extends
to a position opposed to said conveying member.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a recording apparatus which can solve
various problems arising due to the existence of heat, and more
particularly, it relates to a recording apparatus in which the heat
must be considered, for example, such as an ink jet printer having
a thermal fixing means.
2. Related Background Art
To date, ink jet printers have been advantageous in that there was
no need to use a specific fixing means for recording paper.
However, recently, ink jet heads having rapid or prompt response
features and microprocessors capable of performing high speed
operations have been proposed, and high-density multi-orifice ink
jet heads and longer ink jet heads have been developed in
accordance with the progress of high accuracy and/ or super
precision working techniques.
Consequently, the recording speed of the ink jet printer has
rapidly been increased, and thus, some problems which were not
regarded as important up to date have arisen.
In the ink jet printing system, liquid or molten ink drops are
jetted onto a recording paper i.e., recording medium. The fixing of
the ink on the recording medium is effected by the ink penetrating
into the recording medium or by vaporizing the solvent in the ink
(by means of a vaporizing process) to fix the ink pigment on the
recording medium, thereby forming an image on the recording
medium.
More specifically, the ink attached to the recording medium
(normally, a plain paper) is fixed on the recording medium by the
ink penetrating into the medium by capillarity and/or chemical
bonding force, or by leaving the ink pigment or ink dyes on the
recording medium by evaporating the solvent in the ink liquid.
However, in these cases, the fixing speed depends upon not only the
configuration and physical features of the recording medium but
also upon the surrounding atmosphere. Further, the time when the
ink is naturally or unartificially fixed on the recording medium
cannot be reduced beyond a certain limit due to the physical
properties of the ink and medium.
Therefore, in recent high speed printing operations, there has
arisen the problem that the recording medium was ejected before the
fixing of the ink was completed. In such a case, the printer or an
operator's finger is smudged with unfixed ink, or the back of the
next recording paper is smudged with unfixed ink on the previous
recording medium, or an image of high quality cannot be obtained
due to the flow of unfixed ink on the recording medium.
In order to prevent the worsening of the recording quality due to
such imperfect fixing, for example, a special recording medium
(such as coated paper and the like) having an absorbable coating
layer thereon has been used to shorten or decrease the fixing time.
In this case, however, the important advantage that plain paper can
be used in the ink jet printing system is lost, and a new problem
that the use of the special recording paper prevents the wide
development of ink jet printing system arises.
On the other hand, a technique in which the fixing means includes a
heating means for heating the recording medium so as to decrease
the fixing time has also been proposed.
For example, West German Patent Laid-Open Patent No. 2,717,119
discloses a technique in which the thermal fixing is effected by
heating a recorded recording sheet by means of a flat heater. With
this technique, the fixing efficiencY is improved; however, this
proposed technique is still insufficient. That is to say, in this
proposed technique, the heated surface (i.e., the back) of the
recording sheet tends to shrink, thereby curling the recording
sheet. Further, since the front surface of the recording sheet is
supplied with ink liquid by means of the ink jet head, the front
surface of the recording sheet tends to expand due to moisture of
the ink, thus increasing the curl of the recording sheet.
If the recording sheet is so curled, the efficiency of heat
transmission to the recording sheet is considerably decreased;
thus, in order to obtain the desired fixing, the caloric value or
heating value of the heater must be increased. However, the
increased caloric value not only increases the consumption of
energy, but also tends to dry the ink jet head, thus jamming
orifices of the ink jet head. Nevertheless, there was room to
improve the efficiency of the heating and/or to obtain a compact
construction of the ink jet printer.
Further, in recording apparatuses such as ink jet printers and wire
dot printers, the distance between a recording head and a recording
sheet (referred to as "head gap" hereinafter) must be relatively
severely controlled. If the head gap is not maintained properly, in
case of the wire dot printer, since impact force cannot be
maintained uniformly in the printing cycles, there arises a
difference in density between the printed images, and in case of
the ink jet printer, deflected ink dots are recorded on the
recording sheet. Further, if the recording sheet contacts the
printing head, the surface to be recorded (of the recording sheet)
will be smudged.
Therefore, normally, in a recording apparatus, as shown in FIG. 10,
a recording sheet 103 wound around a platen 101 and being fed to a
recording position by means of the platen and pinch rollers 102 is
pressed against the platen 101 just ahead of a recording head 104
by means of a sheet holding plate 105. More particularly, by
pressing the recording sheet 103 against the platen 101 tangential
thereto with uniform force by means of the sheet holding plate 105
the recording sheet 103 is maintained parallel to a face of the
recording head 104, thus ensuring a proper head gap.
Further, in the recent printer market, there has been a tendency
that special use printers have been modified to function as general
use printers (that is, a tendency that the printer is popularized);
for example, a printer which can print or record characters on any
recording sheet has been requested. In this regard, since the wire
dot printer is an impact-type printer, it can easily record the
characters or images even on a plain paper; however, in case of the
ink jet printer, since the ink is used as a printing medium, there
was a problem of the fixing of ink on the recording sheet. Thus, it
has been considered that in the ink jet printer plain paper could
not be used since it was difficult to fix the ink on recording
sheets other than special sheets.
However, recently, various methods and systems for fixing the ink
on the recording sheet have been proposed. Among them, as a fixing
apparatus having a relatively simple and compact construction, an
evaporating fixing apparatus which includes a heater arranged
inside a platen roller or arranged in a paper path other than that
associated with rollers and wherein the fixing is effected by
heating a recorded surface of the recording sheet by means of the
heater to evaporate the moisture in the ink has been put to
practical use. For example, in an apparatus shown in FIG. 11, a
heater 106 is arranged inside a platen 101 and a recording sheet
103 fed by pinch rollers 102 is heated adequately before it reaches
a recording head 104. Alternatively, in an apparatus shown in FIG.
12, a heater 108 is arranged behind a heating plate 107 which also
acts as a flat platen. A recording sheet 103 fed by pinch rollers
102 is pressed against the platen roller 101 by a sheet holding
plate 105 and then is fed to the heating plate 107, where the ink
drops jetted onto the recording paper are vaporized to fix the ink
dyes on the sheet
However, in the above-mentioned printers having a heater, it is, of
course, necessary to provide a sheet holding plate. In these
printers, since the heat is transmitted from the heated recording
sheet to the sheet holding plate, the sheet holding plate is
deflected, as shown in FIG. 13, due to the difference in thermal
strain derived from uneven temperature distribution on the sheet
holding plate. More particularly, in FIG. 13 showing a printer
having a carriage 110 and a heater (not shown) incorporated into a
platen 101, a recording sheet 103 introduced into the printer along
a sheet guide 109 is heated by the heater in the platen 101.
Further, the recording sheet 103 is pressed against the platen 101
by means of a sheet holding plate 105. In this connection, since an
edge 105A of the sheet holding plate 105 is in contact with the
heated recording sheet 103, the edge portion 105A of the sheet
holding plate is locally heated; whereas the remaining portion of
the sheet holding plate is not so heated as the edge portion, since
the heat transmitted to said remaining portion is dispersed through
a frame 111 by which the sheet holding plate 105 is supported.
Consequently, corrugated deflection as shown in FIG. 13 is created
on the edge portion 105A of the sheet holding plate.
In such circumstances, the recording sheet 103 cannot uniformly be
pressed against the platen 101 due to the deflection of the sheet
holding plate, with the result that the recording sheet floats
partly above the platen, thereby causing disorder of the recorded
image, oblique movement of the recording sheet and the like;
further, in this case, if the recording sheet 103 contacts the
recording head, the sheet will be smudged with ink. Of course, such
condition has an undesirable appearance and causes functional
defects.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a
recording apparatus which can solve various problems arising due to
the existence of heat.
Another object of the present invention is to provide a recording
apparatus which achieves high fixing efficiency and can eliminate
the smudge of the recording sheet and the jamming of the nozzles in
the printing head.
It is a further object of the present invention is to provide a
recording apparatus in which the sheet holding plate is not
deflected or distorted.
These and other objects will be apparent from the explanation
provided hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 9 show embodiments of the present invention,
wherein,
FIG. 1 is a perspective view of a recording apparatus according to
a first embodiment of the present invention;
FIG. 2 is a cross sectional end view of the recording apparatus of
FIG. 1;
FIG. 3 is a sectional end view of a recording apparatus according
to a second embodiment of the present invention;
FIG. 4 is a sectional end view of a recording apparatus according
to a third embodiment of the present invention;
FIG. 5 is a sectional end view of a recording apparatus according
to a fourth embodiment of the present invention;
FIG. 6 is a sectional end view of a recording apparatus according
to a fifth embodiment of the present invention;
FIG. 7 is a perspective view of a recording apparatus according to
a sixth embodiment of the present invention;
FIG. 8 is a plan view of a sheet holding plate of a recording
apparatus according to a seventh embodiment of the present
invention;
FIG. 9A is a plan view of a sheet holding plate of a recording
apparatus according to an eighth embodiment of the present
invention; and
FIG. 9B is an end view of the sheet holding plate of FIG. 9A;
FIGS. 10 to 13 shows conventional recording apparatuses,
wherein,
FIG. 10 is an end view of a conventional recording apparatus;
FIG. 11 is a sectional end view of another conventional recording
apparatus;
FIG. 12 is a sectional end view of a further conventional recording
apparatus; and
FIG. 13 is a perspective view of a further conventional recording
apparatus .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be explained with reference to the
illustrated embodiments.
FIG. 1 is a schematic perspective view of an ink jet printer
according to a first embodiment of the present invention. The
printer includes a fixing means (heating means) 1 comprising a
heating portion, a planar surface 1a which constitutes platen,
discharging rollers 2, a paper (recording medium 6) holding member
3, a carriage 4, a recording head 5, and a driving belt 7 for
shifting the carriage.
With reference to FIG. 2 showing a schematic sectional end view of
the ink jet printer of FIG. 1, the printer further includes bail
rollers 8, a friction roller 9, pinch rollers 10 and a paper
(recording medium) guide 11.
In the illustrated embodiment, the recording medium 6 fed from a
direction shown by an arrow A is introduced between the paper guide
11 and the friction roller 9 and is conveyed, by means of the pinch
rollers 10, to a recording portion situated in front of the
recording head 5. After the recording is effected on the recording
medium, the recording medium is directed between the discharging
rollers 2 and the bail rollers 8 and then is discharged from the
printer.
Further, in the illustrated embodiment, while the recording medium
6 left from the friction roller 9 passes through the fixing means 1
which extends from an area including a plane opposed to the
recording head to the discharging rollers 2, the recording medium
is heated by the fixing means and then is discharged from the
printer.
In the illustrated embodiment, by extending the fixing means 1 up
to an area to which the discharging rollers 2 belong, it is
possible to ensure adequate fixing, while maintaining a short
transporting path for the recording medium, and in particular, a
short discharging path.
More specifically, if the transporting path for the recording
medium is shortened or decreased so that it is smaller than that of
the conventional ink jet printer, the effective length of the
fixing means will inevitably be shortened. On the other hand, if
the fixing means cannot provide a fixing time sufficient to perform
a desired fixing due to the insufficient effective length thereof,
there will be no meaning in the provision of the fixing means.
Thus, in the illustrated embodiment, the fixing means 1 is extended
up to the area to which the discharging rollers 2 belong, so that
the required effective length of the fixing means is obtained.
Consequently, in this embodiment, it is possible to perform an
adequate or complete fixing, to obtain a compact construction, and
to obtain a recorded image of high quality regardless of
circumferential environment.
If the fixing means comprises a heat source, the feature of the
fixing depends upon the temperature of the fixing means and the
fixing time (the time when the recorded paper is moving on the
fixing means). For example, if the temperature of the fixing means
is increased, the fixing time may be decreased accordingly.
However, if the temperature of the fixing means is too high, the
recording medium contacting the fixing means will be curled; thus,
in this case, a straightener for flattening the curled recording
medium must be provided. In order to avoid the provision of the
straightener, the apparatus should be designed so that the paper
path (i.e., the transporting path for the recording medium) is so
curved as not to apply undesirable stress to the recording medium
in the paper path. In this connection, in the illustrated
embodiment, the fixing means 1 has an intermediate bent portion of
a predetermined curvature. The temperature of the fixing means is
preferably in the range of 30.degree.-150.degree. C., including the
temperature when the recording medium is applied to special use,
and, in general, is in the range of 40.degree.-100.degree. C. When
an upper limit of the fixing temperature is suitably selected, the
required length of the heater (i.e., an effective length of the
fixing means) can naturally been determined. For example, when a
water-based (water soluble) ink is used, it was found that if the
temperature of the heater was selected to 60.degree. C., 80.degree.
C. and 100.degree. C., respectively, the required fixing time was 5
sec, 3 sec and 2 sec, respectively. This shows that the higher
temperature of the fixing means is preferable to a decrease in the
fixing time. On the other hand, the lower temperature of the fixing
means is desirable to decrease the running cost including electric
power to be consumed, and to achieve a compact construction and a
low price of the recording apparatus due to the use of a
small-sized power unit.
In order to satisfy the above requirements, in the illustrated
embodiment, the discharging or ejecting rollers 2 are arranged to
overlap a portion of the fixing means. With this arrangement, it is
possible to lengthen the fixing means without extending the paper
path.
Next, a second embodiment of the present invention in which the
contact between the recording paper and the fixing means is
improved to effect more effective fixing will be explained with
reference to a sectional end view of the recording apparatus shown
in FIG. 3. In this embodiment, as shown in FIG. 3, the fixing means
1 has an easy or gentle curvature through the whole length thereof
to provide a gentle paper path. With this construction, the contact
between the fixing means 1 and the recording medium 6 is improved,
with the result that the heat transmission from the fixing means to
the recording medium is also improved, whereby a shorter fixing
means can be used with the same fixing temperature.
Incidentally, in this second embodiment, since the fixing means
(heating means) 1 extends up to the ejecting or discharging rollers
2, the temperature in the vicinity of the ejecting rollers 2 is
increased. Thus, the ejecting rollers 2 are preferably formed by
heat resisting material (for example, such as I.R, C.R rubber or
norbornene polymer) in place of conventional roller material (for
example, Urethan). By constructing the ejecting rollers 2 with the
heat resisting and wear resisting material having a high
coefficient of friction, the ejecting rollers 2 can be positioned
nearer the fixing means, thus permitting more compact construction
of the recording apparatus.
In the above-mentioned embodiments, the recording apparatus having
a sing-e fixing means has been explained. However, considering the
thermal or heating efficiency, the cost, the electric power to be
consumed and fixing efficiency, as shown in a third embodiment of
FIG. 4, the recording apparatus may include a first fixing means
11' extending from the recording area to the ejecting rollers 2 and
may utilize a paper guide 11" itself as a second fixing means. Of
course, the position of these fixing means may be determined
synthetically on the basis of the fixing efficiency and the like;
therefore, the position and configuration of the fixing means are
not limited to the illustrated ones.
Further, in the above-mentioned embodiments, as explained above,
fixing is effected by evaporating the solvent in the ink by means
of the heater incorporated in the fixing means. However, as shown
in a fourth embodiment of FIG. 5, a suction force may apply to the
back of the recording medium 6. In this case, the fixing efficiency
can be improved by penetrating the ink into the recording medium 6
more rapidly by means of the suction force, as well as by heating
the recording medium by means of the heater, and the fixing time
can be reduced by promoting the evaporation of the ink solvent due
to the agitation of surrounding atmosphere by means of the suction
force. Further, in this case, the advantage that the recording
medium 6 positively contacts the fixing means (that is, the
floating of the recording medium from the fixing means can be
positively prevented) can also be obtained. In this fourth
embodiment, the fixing means comprises a porous platen 16 having
the heater (not shown) therein, and the suction force is created by
an appropriate negative pressure source or suction source (not
shown).
Further, as shown in a fifth embodiment of FIG. 6, the fixing
efficiency may be improved by providing a heater 15 behind a fixing
means 91 and by forming an air passage in the heater so as to
supply the heated air onto the recording medium. In this case, the
heated air may be directed in a direction in which the recording
medium is moved so that the heated air is not directly applied to
the ink jet head. Further, also in this case, the floating of the
recording medium can be prevented. With this construction, the
fixing efficiency is remarkably improved by radiation from the
fixing means 91 and the heated air from the heater 15.
Next, embodiments of the present invention which can effectively
solve the problem of the thermal deflection or distortion of the
sheet holding plate, among the various problems arising due to the
existence of heat will be explained.
FIG. 7 shows a sixth embodiment of the present invention. In this
embodiment, the recording apparatus includes a platen roller 101
incorporating a heater (not shown) therein, a recording head 104
carried by a carriage 110 which can be shifted along a pair of
guide shafts 112A and 112B by means of an appropriate driving means
(not shown), an ink supplying conduit 113, a flexible cable 114 for
applying an ink jetting signal to the recording head 104, and a
restoring device 115 for preventing the jamming of nozzles in the
recording head 104 to ensure a correct ink jetting operation. A
sheet holding plate 121 of the recording apparatus of this
embodiment has an edge portion 121A which is pressed against the
platen roller 101. The edge portion 105A has a plurality of
parallel notches or slots 122. The depth of each slot 122 and the
distance between the adjacent slots may be suitably selected. For
example, the distance between the adjacent slots 122 may be reduced
if a large amount of heat is transmitted to the edge portion 121A
of the sheet holding plate 121 due to the higher temperature of the
heater. Further, the depth of each slot 122 may be adjusted to
obtain an optimum spring rate of the sheet holding plate 121.
Preferably, the depth of the slot is smaller than half the width
(the length of the plate measured in a direction that the slot
extends) of the sheet holding plate.
With such a construction of the sheet holding plate 121, since the
heat transmitted to the edge portion 121A is dispersed through the
slots 122 and the slots can compensate or absorb thermal expansion
in a longitudinal direction of the sheet holding plate 121, the
edge portion 121A is not deflected even if the thermal strain is
generated thereon, thus maintaining the good contact of the
recording medium 103 against the platen 101.
FIGS. 8 to 13 show other embodiments of the present invention. FIG.
8 shows a seventh embodiment of the present invention, wherein a
sheet holding plate 121 has a recessed upper portion including an
edge 121A which contacts with the platen roller (not shown) and a
slotted or notched lower portion. In this embodiment, a central
tongue 121B formed in the lower portion of the sheet holding plate
121 is suitably fixed, but the other tongues (side tongues) 121B
can be moved laterally in appropriate slots (not shown).
FIGS. 9A and 9B show an eighth embodiment of the present invention,
wherein a sheet holding plate 121 has one or more elongated
projections or beads 125 smoothly protruded from a surface of the
sheet holding plate and positioned parallel to an edge portion 121A
of the plate. With this construction, the same effect as those in
the embodiments of FIGS. 7 and 8 can be obtained. Further, in this
embodiment, since the spring rate of the sheet holding plate 121 is
larger, even a thicker recording medium such as an envelope and a
thick paper can be positively pressed against the platen. In this
embodiment, although the elongated beads 125 have been explained,
the configuration and the number of these projections 125 are not
limited to the illustrated ones, and any projection or projections
can be used so far as it protrudes smoothly from the surface of the
sheet holding plate and does not prevent the advance movement of
the recording medium.
Furthermore, it should be noted that the present invention is not
limited to the ink jet printer or wire dot printer. For example,
the present invention can be widely adapted to a copying machine
and other machines having a fixing means including a heat source
and means for holding a heated sheet and the like, to effectively
eliminate the thermal distortion of the sheet holding plate due to
an uneven temperature distribution thereon.
* * * * *